[llvm] [SystemZ][z/OS] Refactor AutoConvert.h to remove large MVS guard (PR #143174)

[Abhina Sree via llvm-commits]

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@@ -28,16 +29,55 @@
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
+
 int enablezOSAutoConversion(int FD);
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abhina-sree wrote:

I left those guarded for now. The C++ functions are calling the C functions under the covers. 

https://github.com/llvm/llvm-project/pull/143174